Medical images used for diagnosis of cells, pre-clinical study, clinical study, and patients are generally classified into structural images and functional images. The structural images mean the structural and anatomical images of human bodies and the functional images are obtained by imaging functional information on the metabolic functions of the human bodies by using a direct or indirect method. A structural and anatomical imaging technology includes computed tomography (CT) and magnetic resonance imaging (MRI), and positron emission tomography (PET) is being widely used as a technology that images functional information by observing the physiological and biochemical actions of the human bodies.
PET is a powerful biological imaging tool that meters the functions of the human bodies by using a non-invasive method. PET injects, into the human bodies, biological probe molecules labeled as positron emission isotope having radioactive activation, realigns and images the distribution of radioactivity by using tomography to be able to quantify the physiological and physiochemical reactions in each of organs in the human bodies. Functional/molecular information on the structures of the human bodies such as brain and organs provided by PET may be usefully used for finding the cause of a disease, determining a prognosis and observing progress after anticancer treatments.
Also, PET provides functional information on the tissues in the human body with molecule-level sensitivity and its concept is developing to hybrid PET medical imaging equipment such as a PET-CT hybrid device or a PET-MRI imaging device.
FIG. 1 is a diagram for explaining the structure of a typical, cylindrical MRI.
Referring to FIG. 1, a typical MRI machine 100 includes a solenoid coil 150 that uniformly generates a magnetic field, and a magnetic-field correction coil. The direction B, 120 of a magnetic field of the MRI machine 100 is formed in the length direction of a cylinder.
The MRI machine 100 generates a high frequency electromagnetic wave while a human body is in a large cylinder generating the magnetic field, allows hydrogen atoms around the human body to resonate, measures the difference between signals emitting from each tissue, realigns and images the hydrogen atoms through a computer. That is, the MRI machine 100 emits a high frequency electromagnetic wave from its magnet device to a human body, receives it back if a signal such as echo is emitted, converts the signal into position related digital information and makes the digital information as images.
FIG. 2 is a diagram for explaining the structure of a typical, cylindrical conventional PET machine.
Referring to FIG. 2, the typical PET machine 200 has a doughnut-shaped cylindrical structure and includes a PET image sensor electrode 250. The PET image sensor electrodes 250 are formed on the external and internal circumferential regions of a cylinder. Thus, the direction E, 220 of an electric field of the PET machine 200 is formed perpendicularly to the length direction of the cylinder.
After a positron emitted from radioactive isotope is emitted, it exhausts its own kinetic energy for a very short time, combines with a neighboring electron in atom and is annihilated, in which case two annihilation radiations are emitted at an angle of 180□. The PET machine 200 is a module for detecting the two annihilation radiations that are emitted together.
The PET-MRI device has both the function of the PET machine 200 representing 3D physiochemical, functional images of human bodies by using radioactive medicine and medical supplies emitting positrons and the function of the MRI machine 100 performing 3D examination on the tissues and blood vessels of human bodies by using a superconductive magnet and a radio high frequency radio-wave. That is, the PET-MRI device is a hybrid molecular imaging system in which the PET machine 200 showing supersensitive molecular images is combined with the MRI machine 100 showing high-resolution functional images. Accordingly, the PET-MRI device provides enhancement of diagnosis accuracy, a new image bio-marker, new medicine development, a decrease in radiation exposure and enhancement of patient convenience.
Currently, the PET-MRI device includes the PET machine 200 in the MRI machine 100 and uses several methods so that the image sensor of the PET machine is less affected by a magnetic field in an integration process. Among others, it uses a radioactivity reacting material of a scintillator, a photomultiplier tube converting a visible light generated from the material into an electron, or a thin silicon based semiconductor light-receiving sensor.
However, the MRI machine fundamentally fails to remove an effect on a magnetic field in all cases. Thus, it is true that the efficiency of the PET-MRI device decreases.
Korean patent publication No. 2012-0057601 relates to a method of removing noise from PET signal in a PET-MRI hybrid device using filtering and PET machine in a PET-MRI hybrid device using the same.